Polymeric materials are useful as viscosity enhancers when dissolved in the appropriate solvent system. The principal reason for this behavior is due primarily to the large volume which a single macromolecular chain can occupy within the solvent. An increase in the size of the chain produces a concomitant enhancement in the solution viscosity. However, when the polymer chain is placed in a shear field, segmental orientation takes place in the direction of the shearing force. The viscosity of the fluid dramatically drops due to this orientation phenomena. This is a typical behavior of most solutions containing dissolved polymeric materials. However, if the polymer molecule has a high molecular weight with a relatively flexible backbone and the solvent viscosity is sufficiently high, different behavior can be anticipated. It has been shown by several groups that, with increasing shear rates, the viscosity should show a decrease, followed by a minimum value and a small subsequent increase in cases where both solvent viscosity and polymer molecular weight are very high. This latter effect gives rise to a slight dilatant behavior. However, the above-mentioned conditions required for the appearance of a slight shear thickening behavior in these polymeric solution systems are not applicable for many technologically interesting fluids. In most of the common synthetic polymers it is difficult from a synthetic viewpoint to obtain sufficiently high molecular weight and, in addition, most solvents (for example, jet fuels) have rather low viscosities.
Shear thickening behavior can be useful in effecting anti-misting characteristics. Such a solution can behave as a fairly low viscosity fluid at low shear rates. However, the viscosity begins to rise as the shear rate is progressively increased. Accordingly, the solution can more effectively resist breakup into a mist of minute droplets. This is a very desirable attribute in a variety of fluids of technological interest and specifically jet fuels.
In some applications anti-mist action, imparted to a Newtonian liquid by a polymer, must be degraded. For example, anti-mist jet fuel or kerosene (AMK) must be degraded to its original "misting" condition just before combustion in the jet engine. Traditionally this degradation is achieved by subjecting the polymeric solution to very high mechanical shear and breaking the polymeric backbone into low molecular weight polymers which do not impart anti-mist characteristics to the fuel. More recently it has been shown that with certain associating polymers this may be achieved with the addition of low molecular weight polar materials (e.g., alcohols, acids, amines) which disrupt interpolymer associations. In either case, the degradation is difficult to fully realize and the misting characteristics of neat jet are difficult to achieve.